A problem with edges and vertex after smoothing
I am wondering why those edges are hard in the first place. There could be double vertices there. I would make 2 suggestions. The first is to remove doubles in edit mode. Select>Alt M>Merge by distance and set 0.0005 to start with in the operator bottom left. Up the distance a little tiny bit if necessary. The second suggestion is to apply Smooth Shading to your model before you apply any subsurface modifier (right click the body in object mode>choose Shade Smooth) Doing so would have a couple of benefits at this stage. You might find you don't need the modifier and therefore keep it low poly. And, in this case, you would see any pinching or areas that need fixing as they will show up as bad shading.